DESCRIPTION: (provided by the applicant) The long-term objective is to delineate the molecular mechanisms by which neural activity regulates the efficacy and structural integrity of central synapses, and to identify processes that ultimately determine the synaptic connectivity patterns. Many drugs of abuse modulate synaptic activity, and their long-term use is likely to promote remodeling of neural circuitry that contributes to the neurological dysfunction. This proposal seeks to facilitate a search for therapeutic intervention of neural remodeling that accompany substance abuse. Cultured neurons provide a valuable system to study activity-dependent behavior of individual synapses. Long-term observation of individual synapses for correlating activity and structural modifications, however, is hampered by procedural limitations. Stimulation protocols either lack spatial specificity, or require Substantial physiological perturbation to the neuron. The goal of this proposal is to develop a novel non-invasive stimulation technique to examine activity-dependent synapse remodeling of cultured neurons and to implement the technique. I. Photoconductive stimulation of cultured hippocampal neurons The ability of light to alter the conductivity of silicon will be exploited to achieve targeted photoconductive stimulation of dissociated hippocampal neurons cultured on silicon surface. Photoconductive stimulation parameters will be optimized using Ca(2+)-sensitive fluorescent dyes and activity-dependent fluorescent synapse markers. II. Mechanisms of activity-dependent morphological plasticity of synapses formed on silicon The role of activity in inducing short- and long-term morphological changes of hippocampal synapses will be addressed by targeted photoconductive stimulation. Our working model is that stimulus paradigms that are used to elicit long-term potentiation induce new synapse formation. The behavior of synaptic actin dynamics, synaptic vesicle distribution and the stability of postsynaptic density will be examined by real-time video imaging of fluorescent markers, and pharmacological requirements of morphological plasticity will be established. The role of actin dynamics as the potential downstream target of synaptic activation, which initiate the actual process of synapse remodeling, will also be addressed.